Low Flow Inventory

SuAsCo (Sudbury-Assabet-Concord) River Basin

Observations

The Sudbury River ran dry for about 200 feet near Fruit Street in Hopkinton during August and September of 1999 for a period of about 15 days (see photo below) (1).

In the Assabet River subwatershed, Nashoba Brook near Acton is listed by DEM as a “high stress” basin based on its low discharge per square mile of watershed compared to other rivers in the state (2).

Suspected Causes

Water Withdrawals The no-flow event on the Sudbury River near Fruit Street in Hopkinton may have been due to a combination of 1999 drought conditions and numerous groundwater wells nearby. All of the Town of Hopkinton’s wells plus the wells for a golf course are located in the Whitehall area near the Fruit Street section of the Sudbury River. The Town of Westborough has installed a monitoring well at Fruit Street to observe future water levels (1).

The Organization for the Assabet River (OAR) is concerned that the operation of the Howard Street wells in Northborough is depleting stream flow in Howard Brook and possibly impacting the trout fishery there (6). A vernal pool site near a well field in Acton was also nearly dry in early spring of 2002, a time when this pool has been about five feet deep in the past (4).

Elizabeth Brook, a tributary of the Assabet River in Stowe, Boxborough, and Harvard, was too low for water quality sampling during 1999 and members of OAR, among others, worry that streamflow in many tributaries of the Assabet suffer from frequent low flow problems. A quick comparison of withdrawals versus the amount of water in the tributaries during low flow periods revealed many stream sections where water withdrawals exceeded the estimated 7Q10: approximately 140% of the estimated 7Q10 is withdrawn from the A1 impoundment’s subwatershed in Westborough; approximately 85% of the estimated 7Q10 is withdrawn from the Howard/Cold Harbor Brook subwatershed in Northborough; approximately 440% of the estimated 7Q10 is withdrawn from the Fort Meadow Brook subwatershed in Hudson; approximately 450% of the estimated 7Q10 is withdrawn from the Millham Reservoir subwatershed in Marlborough; and approximately 140% of the estimated 7Q10 is withdrawn from the Taylor Brook subwatershed in Maynard (5). OAR recently received an EPA EMPACT grant to study the effects of surface water withdrawals on stream flow in several of these tributaries (3).

Jackstraw Brook in Westborough was observed dry between Westborough's water supply wells on August 12, 2004. Several isolated pools near Upton Road were the last refuge for native brook trout (See photo below), whose presence indicates that this brook was once a high quality cold water fishery. Low flows and heavy sediment loads from upstream development have degraded habitat for aquatic species, and the trout have to congregate in the few remaining pools for survival (11).

Low flows and heavy sediment loads from upstream development degrade habitat for coldwater fisheries in Jackstraw Brook, Westborough (left). Native brook trout survive in isolated pools along Jackstraw Brook (right). September 2, 2004.

Dam Management The Assabet River below the A1 impoundment (also known as Mill Pond) in Westborough runs dry for a length of about 1 mile during dry periods (3,5). When the structure was built for flood control purposes in the 1950’s, there may have been a minimum flow release requirement of 3.5 cfs, but, partly because the impoundment is shallow and does not have much storage capacity to allow releases to improve stream flow, this minimum flow requirement has not been met. Further downstream, seven wastewater treatment plants discharge to the river and actually increase stream flow during dry periods above naturally occurring levels (3). The lowest seven-day average flow (7Q10) at the USGS gaging station in Maynard was 11.6 cfs in August of 1999. During this same month the average wastewater effluent discharge upstream was 12.6 cfs (5). Thus, the wastewater effluent constituted essentially the entire flow of the river at Maynard and was not diluted or augmented by any base flow in the river. This phenomenon of increased discharge during low flow periods due to wastewater effluent can be observed by noting the frequency and magnitude of low flow events on the USGS Water Resources webpage for historic stream flow data at the Maynard USGS gaging station (station #01097000).

References & Resources

1. Linda Hubley. SWAMP. Personal communication with Margaret Kearns, February 2002.
2. Stressed Basins in Massachusetts. Final draft, OWR version 3. 12/01.
3. Sue Beede, Organization for the Assabet River. Personal communication with Margaret Kearns, February 2002.
4. Shep Evans. Personal communication with Margaret Kearns, March 2002.
5. Ronald Manfredonia, Associate Director of Surface Water Programs, Environmental Protection Agency, New England Region. December 8, 2000. Comments on the Environmental Notification Form for the Assabet River Consortium’s Wastewater Management Plan (EOEA file #12348).
6. Organization for the Assabet River. June 2000. Summary of OAR’s Work on Flow Issues, September – present (6/00).
7. USGS historic discharge data for the Assabet River at Maynard
8. USGS real-time stream gage data for the Assabet River at Maynard.
9. USGS real-time stream gage data for the Sudbury River at Saxonville.
10. USGS real-time stream gage data for the Concord River below R Meadow brook, Lowell.
11. Richards, Todd . MA Division of Fisheries and Wildlife. Personal communication with Margaret Kearns, August 12, 2004.